Touch panels are often used on portable electronic devices (e.g., cell phones, PDAs, etc.) for purposes of controlling the device. In the case of a cell phone, the touch panel may include touch sensitive areas or keys for the digits 0-9 as well as touch sensitive areas for specialized purposes such as placing calls or ending calls. In the case of a PDA, the touch panel may include a full QWERTY keyboard as well as ON-OFF functions.
Touch panels are typically constructed with a two-dimensional array or matrix of touch sensitive areas that function as conventional pushbuttons. In some touch panels, e.g., resistive touch panels, several layers of materials, separated by thin spacers, may be used to form the two dimensional array. A surface of the touch panel is typically constructed of a single piece of material that covers the touch sensitive areas. The spacers may surround each of the touch sensitive areas. A user may activate the touch sensitive area by pressing on the surface of the touch sensitive area thereby deforming a top surface of the touch sensitive area towards an underlying layer.
The underside of the top layer may include a capacitive or resistive material that causes a change that is detected by a touch panel interface. Alternatively, the deformation of the top surface may interrupt an optical beam traveling through the touch sensitive area.
In general, each row and column of the array provides an output value. When a user activates a touch sensitive area, the row and column in which the activated touch sensitive area is located provides an output or fails to provide an output depending upon the technology.
The touch panel interface may detect activation of the touch sensitive area via an optical or electrical detector connected to each row and each column of the touch panel. While providing an optical or electrical detector for each row and column is effective, it is expensive. Accordingly, a need exists for simpler methods of identifying activated touch sensitive areas of touch panels.